It is possible to dramatically increase the efficiency of train movements by optimizing the schedule of train movements to account for interactions between trains such as meets, passes, merges, and contention for terminal resources. One approach is embodied in the meet/pass planners incorporated in some current CAD systems. These meet/pass planners are actually decision-aids which assist an operator in making a decision over which train to place on which siding in order to resolve an impending conflict between trains. In Matheson et al. U.S. Pat. No. 5,623,413, issued Apr. 22, 1997, entitled xe2x80x9cScheduling System and Methodxe2x80x9d, a new approach was proposed which provided a detailed schedule for each trains movements over an entire crew shift. Such a schedule is referred to in this document as a train movement plan. A train movement plan is defined as a detailed schedule for each train identifying each track element and switch that the train moves over and the time that such movement occurs.
Preparing a movement plan is a computationally intensive process which requires significant computer resources. Once the plan is prepared, it may be implemented either automatically or manually. Implementation involves coordination between the train crews operating the trains and the dispatcher (controller) who issues movement authorities and controls remotely controlled switches and signals. A movement plan provides the basis for automatically controlling signals and switches and ultimately forms the basis for automatic operation of the trains themselves. If in the course of implementing a plan, deviations from the plan occur, the movement plan may be damaged and no longer provide a solution to all train conflicts. Railroad operations must continue while a new plan is being prepared. A schedule repairer is a means of providing timely alterations to a damaged movement plan to account for deviations from the plan caused by mechanical failure, human failure, unforeseen activities, and incorrect data.
Generally, in prior art scheduling systems, the schedule of operation of the trains is fixed, often months in advance, based upon historic average trip times. Because the schedules are based upon averages it is not possible to schedule the details of meets and passes unless the rail traffic is very light.
Moreover, typical scheduling systems use a fixed set of priorities and routes resulting in only a minimal amount of flexibility to work around problems. These systems do not have the predictive intelligence to plan beyond the next few blocks as monitored by the signal system.
The typical scheduling system used to generate global movement plans utilize simulation techniques with a form of branch and bound search technique to generate conflict free fine grain schedules for the trains within the scope of the scheduling system. These scheduling systems are not amenable to solving the real time deviations experienced in implementing the movement plan due to time constraints. As such, the prior art scheduling systems can not account for conflicts in the schedule which are created due to deviations from the movement plan. Such conflicts are typically resolved through human intervention of the train dispatchers.
For example, a branch and bound based scheduling system may take several hours to generate a global movement plan. Accordingly, such fine grained movement plans may only be generated daily. Such a scheduling system is not capable of resolving conflicts that arise due to the normal deviations experienced in a railway system. Other approaches use a form of decision support tool in which a dispatcher may propose a solution to a conflict and view the ramifications of his solution. Such an approach is limited by the skill of the dispatcher and does not offer the growth to fully automatic operation.
For a further explanation of the utilization and the difficulties associated with scheduling systems, refer to the Matheson et al. U.S. Pat. No. 5,623,413, issued Apr. 22, 1997, entitled xe2x80x9cScheduling System and Methodxe2x80x9d, and having some inventors in common with the present application.
The present invention incorporates predictive schedule repairing which will continuously adjust train routes and controls in real time so that system throughput is optimized. One advantage of this look ahead schedule repairer is that intelligent decisions can be made due to the collection of real time data as well as the use of predictive algorithms which are able to estimate potential conflicts, resolve the conflicts and leave the rest of the movement plan undisturbed in a very short amount of time.
One of the benefits of the present schedule repairer system is the improved throughput over the rail that results from planning efficient train movements. Unlike other approaches which require the entire schedule to be regenerated which can not dynamically revise portions of the movement plan, the present invention can rapidly react to changes in predicted needs and create a revised movement plan within thirty seconds. The schedule repairer constantly receives train performance data and compares that to the movement plan. Adjustments to the train movement plan may be accomplished frequently in order to stay current with the activities on the railway system.
A very important aspect with the use of precision scheduling is the ability to handle deviations from the movement plan when they occur. The most common problem with fixed schedules that are set up far in advance is that conflicts occur which cause elements of the network to get off schedule, and those off-scheduled elements will ripple through the system causing other elements to get off-schedule. For example, the late arrival of a train at a siding may delay the progress of another train which was being met at the siding, and this delay may cause the second train to arrive late for a meet with a third train. This cascading of effects, if not promptly addressed, often leads to track congestion with the result that crews exceed their time of service and terminals become congested with serious reductions in train performance. These ripple effects are common and the standard operating procedures for railroads task the dispatcher with manually taking action to minimize the impact. With the increasing traffic levels on today""s railroads, this task exceeds the capability of all but the most competent dispatchers. Due to time constraints, other scheduling systems, and decision support systems are unable to revise the movement plan in sufficient time to resolve the conflicts while preventing the propagation effects described earlier.
A key element of the train schedule repairer system as provided by the present invention is that it has continuous monitoring of conflicts as they occur, and allows rescheduling to compensate for the presence of these conflicts in the affected portion of the movement plan in a timely fashion. This exception handling capability begins with the conflict being predicted and the available options for the effected trains identified. The available options for the effected trains are evaluated to determine which option will cause the least impact to the rest of the movement plan. Once an option is selected the schedules for the effected trains are adjusted. The movement plan is then evaluated for any conflicts which may have been caused by the adjusted schedules. If a conflict is predicted, the schedule repair cycle just described repeats itself until the adjusted schedules result in a conflict free movement plan. In order to control the number of iterations required to develop a conflict free movement plan, the schedule repair horizon can be constrained so that any conflicts which arise beyond a set time horizon are not resolved in the current repair cycle.
For example, a given train which has deviated from its plan in excess of a predetermined tolerance could cause a conflict that could be corrected simply by small changes to the adjacent trains. On the other hand, an event of a larger magnitude such as a derailment which fouled a given track would cause a large scale rescheduling including the determination and evaluation of multiple options affecting the entire railway system within the scope of the schedule repairer. Such large scale rescheduling would require system wide replanning and course adjustments to the movement plan beyond the scope of the schedule repairer. In such a situation the schedule repairer takes action to minimize the development of future congestion caused by the event. Such action might cause the schedule repairer to direct a train to a siding at its current position rather than allowing it to continue progressing in its trip plan and thereby creating future congestion.
There is a temporal aspect to this rescheduling activity in that the conflict being reported must be acted on immediately for safety reasons, without the determination and evaluation of available options. Once the conflict is acted upon, the schedule repair can determine the options available based on this recently initiated safety action. For example, if a train derails on a segment of track, the schedule repairer may direct that trains in close proximity that may block access to the scene be stopped prior to determining the effect of the loss of the track on the overall movement plan. Moreover, the schedule repair can ensure that the track segments leading up to the derailment location are kept clear of traffic to allow repair apparatus rail access to the derailment location. However, the schedule repairer would not be used to make large scale revisions to the global movement plan. Rather a course scheduler could be used to make large changes to the movement plan before the schedule repairer makes the necessary fine grain revisions to avoid any potential conflicts due to the large scale revision. Thus, the conflict resolution or exception handling process can be involved in various levels of a hierarchial planning system in time sequence until the conflict is fully resolved.
In the typical scheduling system, the most common effect of an unexpected event is to negate large portions of a predetermined schedule. Unfortunately, events happen with great frequency, some of them as small as loss of one locomotive in a three locomotive consist, which causes that train to have two thirds the power for which it had been scheduled. Or deviations from a movement plan are created because the engineer has not attempted, or been unable, to stay on schedule. Without regard to the cause, they occur with great frequency and as a result most freight railroads do not maintain any sort of close coupling with predetermined schedules.
In the schedule repair process it is important to understand the total scope of what is necessary to actually achieve the optimal plan. In the schedule repairer, once a conflict is predicted various options are evaluated. Generally, the option which impacts the rest of the movement plan the least is selected. However, optimization plans can be factored in where certain elements of the operation (certain trains or certain types of shipments) are given a higher priority than others because of the fact that they are considered to be more time critical. These type of business rules can be considered when the options are selected.
Accordingly, it is an object of the present invention to provide a novel method of making fine grain revisions to a movement plan.
It is another object of the present invention to provide a novel method of identifying conflicts that arise due to deviations from the movement plan.
It is yet another object of the present invention to provide a novel method of evaluating the effect of various options on the overall movement plan.
It is still another object of the present invention to provide a novel method of selecting the options which minimize the impact on the rest of the movement plan.
It is yet a further object of the present invention to provide a novel method of evaluated the adjusted schedules of individual trains to determine whether conflicts are predicted.